Corrosion resistant coating

ABSTRACT

A process has been developed which will provide a product that simulates zinc phosphate by providing a corrosion resistant coating on materials including but not limited to, steel, hot dipped galvanized or electrogalvanized metal. The simulated product provides very similar, if not the same, physical and visual attributes as zinc phosphated materials. The process is one, which does not require a convention chemical tank, as it can be roll applied, thereby allowing for broader applications.

FIELD OF THE INVENTION

The present application relates to corrosion resistant coatings, similarto zinc phosphate coatings, a process for their production, and theapplication of said coatings. These coatings may be used on galvanizedand similar metal surfaces.

BACKGROUND OF THE INVENTION

Commercially available baths for producing corrosion resistant phosphatecoatings were developed during the turn of the century. Iron and steelparts were immersed in a phosphoric acid bath containing iron filings.After approximately two hours, a conversion coating was produced thathelped in retarding corrosion.

The coatings are widely used for one or a combination of the reasons,such as to prolong the life of an organic coating; to provide excellentpaint or solid film lubricant resin bonding; to improve corrosionprotection by providing a good base for absorbing and retaining rustpreventing materials; and to provide an excellent base for lubricantsand drawing compounds.

Present day phosphate coating solutions are dilute aqueous solutions ofphosphoric acid and other chemicals which, when applied to the surfaceof a metal react with the metal surface forming an integral layer on thesurface of the metal of a substantially insoluble phosphate coating,amorphous or crystalline. Generally, the crystalline coatings arepreferred.

Typically the solutions include phosphate ions, zinc and other metalions to provide specific characteristics desired in the final coating.Other ions typically present may be nitrate, nitrite, chlorate,fluoroborate or silicofluroride. A typical phosphating process iscomprised of the following sequence: (1) cleaning and conditioning, (2)phosphating and (3) post treating. Rinses are generally employed betweeneach step to prevent any carry over of materials to the next step.

U.S. Pat. No. 4,838,957 describes a zinc phosphating process employingaqueous phosphate solution containing zinc ion, phosphate ion, manganeseion, fluoride ion and a phosphating accelerator.

In U.S. Pat. No. 4,865,653 phosphate coating solutions are described inwhich the accelerator employed is hydroxylamine sulfate, which isemployed so as to alter the morphology of the resulting coating fromplatelet to a columnare and/or nodular structure.

U.S. Pat. No. 5,261,973 discloses zinc phosphate coatings for metalsurfaces and phosphating process. Concentrates containing (a)hydroxylamine sulfate and (b) zinc, nickel, manganese and phosphate ionsare formulated into aqueous coating solutions for treating metalsurfaces, including ferrous, zinc and aluminum surfaces.

However, all the processes provide for the use of convention chemicaltanks. Accordingly, a need exists for a process that would simulate thezinc phosphate coatings, but which would not require the use of achemical tank, but can be roll applied, therefore having broader use,such as to coil coaters and metal coating lines.

SUMMARY OF THE INVENTION

The present application relates to corrosion resistant coatings, similarto zinc phosphate coatings, a process for their production, and theapplication of said coatings. These coatings may be used on galvanizedand similar metal surfaces.

A process has been developed which will provide a product that simulateszinc phosphate by providing a corrosion resistant coating on materialsincluding but not limited to, steel, hot dipped galvanized orelectrogalvanized metal. The simulated product provides very similar, ifnot the same, physical and visual attributes as zinc phosphatedmaterials. The process is one, which does not require a conventionchemical tank, as it can be roll applied, thereby allowing for broaderapplications.

According to one embodiment, a product which simulates zinc phosphatecoatings is comprised of a combination of a polymer, dye and silica. Inaddition to those components, water may also be included in thesimulated material.

In a further alternative embodiment of the invention, the mixture isagitated and applied to a piece of metal either by a roll coater, or bya flood and squeegee method.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. Changes to and substitutions of the variouscomponents of the invention can of course be made. The invention residesas well in sub-combinations and sub-systems of the elements described,and in methods of using them.

DETAILED DESCRIPTION OF THE INVENTION

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, is not limited to the precise valuespecified. In at least some instances, the approximating language maycorrespond to the precision of an instrument for measuring the value.Range limitations may be combined and/or interchanged, and such rangesare identified and include all the sub-ranges included herein unlesscontext or language indicates otherwise. Other than in the operatingexamples or where otherwise indicated, all numbers or expressionsreferring to quantities of ingredients, reaction conditions and thelike, used in the specification and the claims, are to be understood asmodified in all instances by the term “about”.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article or apparatus that comprises a list of elements is notnecessarily limited to only those elements, but may include otherelements not expressly listed or inherent to such process, methodarticle or apparatus.

A process has been developed which provides a product that simulateszinc phosphate on materials including but not limited to, steel, hotdipped galvanized or electrogalvanized metal. The simulated productprovides very similar, if not the same, physical and visual attributesas zinc phosphated materials. The process is one, which does not requirea convention chemical tank, as it can be roll applied, thereby allowingfor broader applications.

In one embodiment of the invention, polymer material, dye and silica arecombined, with water, agitated and then applied to the material to becoated. The polymer to be used can be one of many available and known inthe art, particularly those that are film forming polymers. Examples ofsuch film forming polymers includes, but is not limited to, acrylicpolymers, such as polyacrylates and methacrylates, polyflurocarbons,vinyl ether copolymers, and poysaccharides. In addition, the filmforming polymers may be formulated in a compound that includesadditional components. For instance, included in the polymer componentwould be polymers that are combined with lubricants. A polymer materialthat is blend of an acrylic polymer and lubricants, is an acceptablecomponent for this process and the resulting product. An example of sucha material is BRUGAL GM4-SRF(A)™, which is a proprietary blend of anacrylic polymer and lubricants (ProCoat, Inc., Barcelona, Spain).

An additional component of the present invention a dye or pigment whichis used in an amount sufficient to result in providing the simulatedmaterial the proper hue, so that the material treated with the simulatedzinc phosphate treatment has the same visual attributes as a materialsactually treated with zinc phosphate. Any dye that is known within theart would be acceptable, and combination of dyes would work as well.Examples of the same include, but are not limited to, carbon black,ceramic, titanium dioxide, and combinations thereof. In addition to juststraight dyes, the dye component can be added as a combination. Forinstance, one product that is a combination of a dye and polymer thatcan be used is BRUGAL GM4-SRF(A) Black (ProCoat, Inc., Barcelona,Spain). Depending on the coating weight applied, the coating appearancewill vary from grey to black.

In addition to the polymer and dye, silica is a component of thesimulated zinc phosphate material. The silica is added to increase theadhesion of the current product to the metal to which it is to beapplied. Any silica may be used, with the preferred form to be granularwith a particle size of from about 2 to about 10 microns, preferablyfrom about 5 to about 7 microns. An example of such a silica is Davisil®(Grace Davison, Deerfield, Ill.). As an alternate embodiment, any inertparticle that has a particle size of from about 2 to about 10 micronswould most be able to be substituted for the silica, and would be knownto those skilled in the art.

An additional material that may be part of the simulated zinc phosphatecoating is a passivation agent. Any such agent would work, including butnot limited to chromium, zirconium, titanium or cerium salts, silanes,and combinations thereof. Included as well, would be combinations orsolutions of the agents, such as a phosphochromate solution. An exampleof such a material is BRUGAL GM-4(B)™, which is a proprietary blendcomprising chromic acid, chromium oxide, zinc salt and phosphoric acid(ProCoat, Inc., Barcelona, Spain).

The above components are combined by stirring or agitation. Oneembodiment of the invention provides for the combination of threeinitial ingredients in a ratio. The polymer may be present in an amountof from about 50 to about 70 percent by weight, preferably from about 55to about 65% by weight. The second ingredient, the passivation agent,may be present in an amount of from about 10 to about 20% by weight,preferably from about 12.5 to about 17.5% by weight. The dye or pigmentis present in an amount effective to provide the desired end color. Formost uses, it may be present in an amount of from about 20 to about 30%by weight, preferably from about 22.5 to about 27.5% by weight.

After the three initial ingredients have been combined to form a mix,the silica is then added. The silica should be added in an amount offrom about 0.2 to about 1.0 pounds of silica per gallon of the mix. Themixture containing the silica is agitated and then water may be added toget a to a useable consistency. Water may be added as appropriate toinsure that the coating is of the correct consistency to allow for rollcoating or flow and squeegee application.

The resulting mixture may then be applied to the material to be treatedeither by a roll coater or by flow squeegee method, both of which areknown in the art. The mixture should be applied as a thin coat, and maybe applied to metal, including galvanized or similar metal surfaces,typically through a chemcoater and then cured. The result is a corrosionresistant coating that has lubricating and anti-fingerprintingproperties. An additional benefit to this process is the lack ofrequirement of a post treatment step. In conventional zinc phosphateprocesses, where the coating is applied through a chemical tank, a posttreatment rinse step may be employed. The present process eliminates theneed for such a step.

While the present invention has been described with references topreferred embodiments, various changes or substitutions may be made onthese embodiments by those ordinarily skilled in the art pertinent tothe present invention with out departing from the technical scope of thepresent invention. Therefore, the technical scope of the presentinvention encompasses not only those embodiments described above, butall that fall within the scope of the appended claims.

1. A corrosion resistant coating comprising (a) a film forming polymerin an amount of from 50 to 70% by weight selected from acrylic polymers,polyfluorocarbons, vinyl ether copolymers, poysaccharides or blends ofan acrylic polymer and lubricants; (b) dye selected from carbon black,ceramic, titanium dioxide, and combinations thereof; (c) silica; (d) apassivation agent selected from chromium salts, zirconium salts,titanium salts, cerium salts, silanes, and combinations thereof; and (e)water; wherein the dye is effective to create on a material treated withthe corrosion resistant coating a similar appearance as a materialactually treated with a zinc phosphate.
 2. (canceled)
 3. The corrosionresistant coating of claim 1 which can be roll applied or flow squeegeeapplied.
 4. (canceled)
 5. (canceled)
 6. The corrosion resistant coatingof claim 1 wherein the polymer is present in an amount of from about 55to about 65% by weight.
 7. (canceled)
 8. The corrosion resistant coatingof claim 7 wherein the passivation agent is present in an amount of fromabout 10 to about 20% by weight.
 9. The corrosion resistant coating ofclaim 7 wherein the passivation agent chromate is present in an amountof from about 12.5 to about 17.5% by weight.
 10. The corrosion resistantcoating of claim 1 wherein the dye is present in an amount of from about20 to 30% by weight.
 11. The corrosion resistant coating of claim 1wherein the dye is present in an amount of from about 22.5 to about27.5% by weight.
 12. A process for producing a corrosion reducingcoating comprising (a) mixing together a polymer which is a film formingpolymer in an amount of from 50 to 70% by weight selected from acrylicpolymers, polyfluorocarbons, vinyl ether copolymers, polysaccharides orblends of an acrylic polymer and lubricants, a passivation agent and adye, (b) adding silica to the mixture of step (a) in an amount of fromabout 20 to about 100 grams of silica per liter of the mixture (about0.2 to about 1.0 pounds of silica per gallon of the mixture); and (c)agitating the mixture of step (b).
 13. The process of claim 12 whichfurther comprises applying the mixture from step (c) to a material to betreated.
 14. The process of claim 13 wherein the material to be treatedis chosen from the group comprising steel, hot dipped galvanized orelectrogalvanized metal, or combinations thereof.
 15. The process ofclaim 13 wherein the application is carried out by roll coater or a byflow squeegee method.
 16. The corrosion resistant coating of claim 1further comprising a pigment.
 17. The corrosion resistant coating ofclaim 16 wherein the dye or pigment is effective to create on a materialtreated with the corrosion resistant coating a similar appearance as amaterial actually treated with a zinc phosphate.